[mattigames]

That was not the question, I'm only interested in the possibilities to avoid gps tracking not any other mistakes the killer might have done.

[mystified5016]

Just pull the fuse on the infotainment systems. Disconnect the antennas and pull the Sim card.

GPS jammers are (AFAIK) quite illegal in most places and buying one will attract much more attention than modifying your car in your garage.

[OptionOfT]

While I fully support the privacy measures, I'd like to add a couple of caveats:

1) current cars have eSIMs embedded in the modules, no way to remove them.

2) assuming you can disable the (e)SIM, you also disable the eCall system. Although BMWs allow you to upload your own eSIM, I'm not sure which one is used for eCall / other services.

3) Disabling the MMI these days is fraught with peril, as they run the driver's display (speed, rpm etc) as well.